Project Concept: A Special Table
I want to design and build a special table for myself. The main feature is a hollow center, which can be used to hold plants, creating a small indoor garden. The design also incorporates openings, allowing small pets like cats and dogs to peek through or move around. Although the CAD sketch is simple, it features some interesting and effective joints that allow for a clean and sturdy assembly.
Assignment Overview
This week focuses on computer-controlled machining, working with large-scale fabrication tools like CNC mills, routers, and other automated machining equipment. The goal is to understand the capabilities and limitations of these powerful tools for creating precise, large-scale projects.
Learning Objectives
The main objectives for this week include:
- Understanding computer-controlled machining processes
- Learning to work with CAM software for toolpath generation
- Exploring material properties and machining considerations
- Safety protocols for large-scale machining equipment
- Design considerations for CNC fabrication
Machine Operation and Safety Training
Before beginning fabrication, I completed comprehensive training on operating the ShopBot CNC router, following protocols established in previous years of the How to Make Almost Anything course. The training covered essential safety procedures, including proper emergency stop locations, spindle operation, and dust collection system management. I learned the importance of secure material fixturing—even small movements during cutting can ruin a part or damage the tool.
The machine operation workflow involves several critical steps: First, the material must be surfaced flat and secured with screws placed outside the cutting area. Next, the Z-axis zero point is set by carefully lowering the bit to touch the material surface. The X and Y coordinates are established relative to a corner or datum point on the workpiece. Before running the full program, I learned to perform a "dry run" with the spindle raised to verify the toolpath doesn't collide with clamps or exceed the material boundaries.
Understanding feeds and speeds is crucial for successful machining. Too fast, and the bit can break or burn the material; too slow, and you risk excessive tool wear and poor surface finish. For plywood, I used conservative settings: 12,000 RPM spindle speed with a feed rate around 3-4 inches per second for roughing passes, and slower finishing passes for clean edges.
Process Documentation
The fabrication process began by translating my CAD design into toolpaths using CAM (Computer-Aided Manufacturing) software. I carefully planned the cutting strategy, considering tool diameter, step-over distance, and cutting depth to achieve clean edges and minimize material waste. The plywood sheet was secured to the CNC bed using screws and alignment fixtures, ensuring it would remain stable throughout the multi-hour machining operation.
I selected appropriate feed rates and spindle speeds based on the material properties and tool specifications. The CNC router used a 1/4" end mill for the detailed joint profiles and a larger bit for roughing out the main openings. Throughout the process, I monitored chip evacuation and listened for any unusual sounds that might indicate tool wear or material issues. Safety was paramount—I wore hearing protection, safety glasses, and ensured the dust collection system was running effectively.
The following images document each stage of the machining workflow, from initial setup through final assembly of the custom joints.
